(1) Field of the Invention
The present invention relates to an exhaust system for a motorcycle which have a V-type multi-cylinder engine such as a V-type two-cylinder engine mounted thereon, and more detailedly relates to an exhaust system for a motorcycle wherein joining between front and rear exhaust lines being in communication with each other and assembly of mufflers to the motorcycle body are taken into consideration.
(2) Description of the Prior Art
As one example of a conventional exhaust system for a motorcycle of this type, a first exhaust pipe 2A is extended from the exhaust of the front cylinder 1A side of a V-type two cylinder engine unit 1 mounted on a vehicle body A and connected to a first muffler 3 forming a forward exhaust arrangement while a second exhaust pipe 2B is extended from the exhaust of the rear cylinder 1B side and connected to a second muffler 4 forming a backward exhaust arrangement, and these first and second mufflers 3 and 4 are assembled to one side of vehicle body A, as shown in FIG. 1.
When such an exhaust system is assembled to vehicle body A, second muffler 4 is arranged above and shifted behind, with respect to first muffler 3, as shown in FIG. 2, so that the two are assembled parallel to each other while in order to enable effective use of mutual exhaust interference, a communicating pipe 5 is provided so as to create a connection between a first expansion chamber 31 on the entrance port 3a side of an expansion chamber 30 of first muffler 3 of the front cylinder 1A exhaust line and second exhaust pipe 2B of the rear cylinder 1B exhaust line, or between first exhaust pipe 2A and second exhaust pipe 2B in their halfway points, though not shown.
However, in the exhaust system having the above conventional configuration, the distance from the position at which communicating pipe 5 is joined to first exhaust pipe 2A to the entrance port 4a of second muffler 4 is rather long, or the distance from the joined point of first exhaust pipe 2A to entrance port 3a of first muffler 3 differs too much from that from the joined point of second exhaust pipe 2B to entrance port 4a of second muffler 4 when first exhaust pipe 2A and second exhaust pipe 2B are connected, so that it is impossible to utilize mutual exhaust interference in an effective enough manner.
Further, when first and second mufflers 3 and 4 are assembled to vehicle body A, the middle part of first muffler 3 but rather closer to the rear end and the middle part of second muffler 4 but rather closer to the front end are joined and welded by means of a bracket 61 and the more or less middle part of first muffler 3 is attached to vehicle body A by means of a bracket 62, as shown in FIG. 2 Alternatively, as shown in FIG. 3, first muffler 3 is attached to vehicle body A at its front and rear points by means of first and second brackets 61 and 62 while the front part of second muffler 4 is attached to vehicle body A by means of a third bracket 63.
The assembly configuration shown in FIG. 3 not only has difficulties in assembling first and second mufflers 3 and 4 to vehicle body A but needs more assembly parts and hence costs more.
In the assembly configuration in FIG. 2, since second muffler 4 is fitted to vehicle body A, at position nearer to the front, the extension of second muffler 4 from its fitted position to the rear is too long. Therefore, excessive stresses are liable to concentrate on the fitted point of second muffler 4 when vehicle body A vibrates or from other reasons, thus prevention of the durability degradation of the second muffler is sought.
The present invention has been devised in view of the above situations, and it is therefore an object of the present invention to provide an exhaust system for a motorcycle which enables effective use of mutual exhaust interference and still allows for easy assembly to the vehicle body.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, an exhaust system for a motorcycle in which a fore-and-aft V-type engine having front and rear cylinders arranged in a V-angled to each other along the front-to-rear direction of the vehicle body is mounted, wherein the first exhaust line from the front cylinder includes a first exhaust pipe which is extended from the front side of the front cylinder, creating a forward exhaust arrangement while the second exhaust line from the rear cylinder includes a second exhaust pipe which is extended from the rear side of the rear cylinder, creating a backward exhaust arrangement, and the first and second exhaust pipes originating from the front and rear cylinders are connected to the respective front-end entrance ports of the first and second mufflers which are arranged below and above on one side, either right or left, in the rear-half of the vehicle in cylindrical shape, so as to be parallel to each other, while the first and second exhaust lines are connected to each other by a communicating pipe, and is characterized in that the first and second mufflers are arranged so that the second muffler is shifted behind with respect to the first muffler while the communicating pipe is arranged so that one end thereof is joined to the peripheral surface of the muffler cylinder corresponding to the first expansion chamber of the first muffler and the other end is connected in parallel with the second exhaust pipe to the front-end entrance port of the second muffler corresponding to the first expansion chamber of the second muffler.
In accordance with the second aspect of the present invention, the exhaust system for a motorcycle having the above first feature is characterized in that the first muffler has a double-wall configuration made up of inner and outer cylinders and a through-connection element which passes through the inner and outer cylinders to allow for communication with first expansion chamber is arranged at the position on the peripheral surface of the first muffler outer cylinder to which the communicating pipe is joined, and in that the connecting end of the communicating pipe has an opening greater in diameter than that of the opening of the through-connection element formed on the periphery of the muffler outer cylinder and is attached to the peripheral surface of the muffler outer cylinder so that the opening of the communicating pipe at the connecting end covers the opening of the through-connection element.
In accordance with the third aspect of the present invention, the exhaust system for a motorcycle having the above first feature is characterized in that the first and second mufflers are coupled integrally by the communicating pipe in the front and also by a second bracket in the rear while a first bracket is provided in the forepart of first muffler which is located ahead, so that the mufflers are fitted and supported on the vehicle body by both the first and second brackets.
In accordance with the fourth aspect of the present invention, the exhaust system for a motorcycle having the above second feature is characterized in that the first and second mufflers are coupled integrally by the communicating pipe in the front and also by a second bracket in the rear while a first bracket is provided in the forepart of first muffler which is located ahead, so that the mufflers are fitted and supported on the vehicle body by both the first and second brackets.